Deconstructing a Green Claim

What Microsoft Says
"Every 10 PCs with CRTs migrated to Windows Vista and configured to use Power Management is equivalent to taking one car off the road in terms of greenhouse gasses."

Back Story
In an era of alarming TV footage of melting glaciers and more personally alarming prices at the gas pump, both consumers and business buyers are citing environmental considerations and energy costs in their purchasing decisions. Seizing on this green mood, Microsoft has taken to repeating the "10-PCs-to-one-car" factoid in its pitch for Windows Vista adoption. This particular claim appears on a Microsoft Web site called "Windows Vista for the Enterprise/Windows Vista Facts"; Brad Brooks, corporate vice president for Microsoft's Online Services and Windows Business Group, cited the same formula in a May webcast. The foundation for the statement is contained in Microsoft's October 2006 white paper, "Windows Vista Energy Conservation."

Microsoft's Assumptions

The per-PC carbon dioxide reductions are derived by comparing Windows Vista against Windows Vista. In one case, the Windows Vista system is left running all the time. In the other case, it's running 10 hours per day, five days per week, and otherwise is in sleep mode. These comparisons do not involve Windows XP or any other operating system.

Calculations were based on Windows Vista running on a "typical" Pentium 4 with a 17-inch CRT monitor or a 17-inch LCD monitor.

Microsoft used a U.S. Environmental Protection Agency estimate that generating 1 kilowatt hour (kWh) of electricity in the United States results in 1.55 pounds of carbon dioxide emissions. Under Microsoft's model, the CRT system saves 760.14 kWh per year, while the LCD systems saves 597.52 kWh per year.

An EPA estimate puts the average carbon dioxide emissions of a car at 11,560 pounds per year.

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Is It True?
In a strict sense, the statement is supportable. It's the implications that get messy.

For one thing, the assumptions are based on CRT and LCD systems in an era when laptop sales are overtaking PC sales.

Presumably the savings aren't as dramatic on laptops, which tend to have much lower power requirements. Laptop figures aren't included in the white paper.

By using the phrase "migrated to Windows Vista" in the marketing message, the implication is that these savings are measured against Windows XP. As the assumption section shows, Windows XP is not involved in the calculations in any way. In other words, there may be a legitimate savings, but it is not measured by this paper.

Windows Vista has also been criticized as being more power hungry than Windows XP because of the significant delta in hardware requirements for Windows Vista when compared with Windows XP.

As often happens, the marketing message has spun away from the conditional facts that support it. Within the white paper, the statement is "Ten of these [Windows Vista] PCs left on when not in use results in the equivalent of one more car on the road in terms of greenhouse gas contribution annually."